In particular, a rod of this kind may be used for effecting metal coating, such as nickel-plating, inside a tube.
In the case of tubes of great length and small diameter, for example in the case of a steam generator tube in a pressurized water nuclear reactor, whose inside diameter is close to 0.02 meter and which comprises two straight portions whose length is greater than ten meters, it may be necessary to effect metal coating, such as nickel-plating, in certain zones of the tube in order to improve its resistance to corrosion during operation.
A treatment of this kind is very often applied to a zone of the tube situated at the outlet face of the tube plate, i.e. a short distance from one of the inlets of the tube, this distance being less than one meter.
It may however be desirable to treat the inner surface of the tube in one of its straight portions at any distance from the inlets of this tube which are flush with the inlet face of the tube plate.
Rods for the treatment of the inside surface of steam generator tubes must be provided with sealing devices enabling the part of the tube to which the treatment is applied to be isolated from adjacent zones, in order to avoid leakages of electrolyte on each side of the zone treated.
Treatment rods of this kind which incorporate sealing devices have been used fairly commonly for the treatment of zones of the tube which are situated inside or near the tube plate. The rod effecting the treatment is supported and centered in the tube being treated by means of its base, which comprises a plurality of centering elements adapted to be introduced into tubes adjoining the tube to be treated. The base member of the rod also incorporates means for effecting the distribution of fluid in the rod, particularly the fluid used for the treatment. A treatment rod of this kind and the sealing device associated with it are of complex structure and consist of numerous parts, so that it is difficult to ensure their correct operation, and leakages of electrolyte liquid may occur at the ends of the zone to be treated.
In addition, a device is known which enables any zone of one of the rectilinear portions of the tube to be treated, and which incorporates a set of braces which must be installed in the tube in proportion as the rod is introduced into the latter. This rod incorporates sealing means consisting of inflatable seals the utilization of which is complex.